A fogbank is the least useful location for a telescope, yet today's space observatories effectively operate inside one. That's because Venus, Earth and Mars orbit within a vast dust cloud produced by comets and occasional collisions among asteroids. After the sun, this so-called zodiacal cloud is the solar system's most luminous feature, and its light has interfered with infrared, optical and ultraviolet observations made by every astronomical space mission to date.

Source: NASA's Goddard, Glenn Centers look to lift space astronomy out of the fog